Electrical resolver means



1966 G. v. A-. MALMROS 3,

ELECTRI CAL RESOLVER MEANS Filed Dec. 31, 1962 FIG.10

FlG.1b

VOLTAGE FIG. 2b SIN B cos 0 90 [$0 270 360 INVENTOR.

I 2 5 4 GUSTAV v. A. MALMROS SIN 2c BY ATTORNEY United States PatentOffice 3,290,495 Fateritetl. Dec. 6, l 966 3,290,495 ELECTRICAL RESGLVERMEANS Gustav V. A. Malmros, Binghamton, N.Y., assignor to InternationalBusiness Machines Corporation, New York, N.Y., a corporation of New YorkFiled Dec. 31;, 1962, Ser. No. 248,490 Claims. (Cl. 235186) The presentinvention relates generally to an .electromechanical potentiometer andtrigonometri resolver devices, and more particularly to a new andimproved resistance type electrical resolver utilizing a flatresistively coated surface.

In the electrical analog and industrial control field, wide use is madeof electro-mechanical otentiometers and trigonometric resolvers. Theelectrical resolvers in use vary in construction over a wide range. Someof the considerations with respect to the selection of a particularresolver for use are related to its mechanical simplicity, its highresolution in the derivation of variable voltages and the uniform torqueloading of the shaft which is driving the resolver for various shaftangles. One type of electrical resolver known in the prior art is onewhich is classified as a resistance resolver in that it resolves a shaftangle position into trigonometric voltage functional relationships byreason of variations of resistance which result from variations in theshaft angle positions. Such prior art resistance resolvers tend to becomplicated mechanically, have poor resolution and present irregulartorque loading to the shaft driver.

It is the variable resistance electrical class to which the teachings ofthe present invention are related. In recent years, technology hasadvanced to the point that it is now possible to deposit or otherwiseapply resistive coatings on substrates. Patent Number 2,542,478, issuedFebruary 20, 1951, is illustrative of the state of the art in theutilization of resistive coatings on fiat surfaces. In keeping with thestate of the art capability in the manufacture of resistance coatings onsubstrates, it is now possible to make substan tial strides in thedesign of electrical resistive type shaft angle trigonometric resolvers.One of the requirements of electrical resolvers used in analog computersand industrial control fields, however, is that it be operative over 360degrees of angular rotation of a shaft. It is, therefore, a primaryobject of the present invention to provide a new and improved resistiveelectrical shaft angle resolver which is rotatable through 360 degreesof shaft angle.

It is still another object of the present invention to provide a new andimproved shaft angle resistive electrical resolver which provides bothsine and cosine trigonometric functional relationships in response to360 degrees shaft rotation.

It is still another object of the present invention to provide a new andimproved resistive electrical resolver which will derive functionaltrigonometric signals commensurate with shaft angle position through 360degrees and at the same time provide electrical signal polarityinformation commensurate with the quadrant through which the shaft angleis being rotated.

The foregoing and other objects of the present invention are obtained byconstructing a shaft angle electrical resolver to include a shaftrotatable through 360 degrees driving at least one Wiper arm pivotallymounted at one extremity relative to a flat surface having a resistivecoating placed thereon so that a wiper contact mounted on the otherextremity of each of the wiper arms maintains slidable conductivecontact on the resistive coating and at the same time is positioned asto its pivotal mounting and the length of the wiper arm such that theWiper contact makes physical conductive alternate contact with the twoparallel electrodes at 180 degree angular positions of the shaft.

The resistive coating is energized by applying a voltage source acrossthe two parallel electrodes.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings.

In the drawings:

FIGURES 1a, 1b and 1c illustrate the mechanical construction and theelectrical output of a resistive resolver according to one embodiment ofthe teachings of the present invention; and

FIGURES 2a, 2b and 2c illustrate the mechanical construction and theelectrical output of a second embodiment of an electrical resolver builtaccording to the teachings of the present invention.

Referring to FIGURES la and 11), there is shown a flat surface 10consisting of a substrate material of an insulating type havingdeposited thereon a uniform film or coating 11 of resistive material.For example, this uniform film or coating of resistive material may havea resistance of 10,000 ohms per square (unit area). This coating or filmcan be done in several ways now known to those skilled in the art. Forexample, the film 11 may be the result of the deposition of metallicsalts which are fired in a manner to provide a reasonable wearingresistive surface. As shown, located at opposite extremities of theresistive coating 11 are two conductive strips or electrodes 12 and 13.These conductive strips are substantially parallel and should providehighly conductive connections to the resistive surface. These conductivestrips or electrodes can be made by depositing or plating, etc., suchmaterials as gold or copper, etc.

Mounted for pivotal rotation adjacent the resistive surface 11 is showna non-conducting wiper arm 14. Mounted on the non-pivoting extremity ofthe arm 14 is a wiper contact 15 which is designed to conductivelycooperate with the resistive surface 11 as the wiper arm 14 is rotatedby shaft 16. As the shaft 16 is rotated through 360 degrees, the wipercontact 15 will make contact with the resistive surface 11 along a pathshown therein as a circle. The position at which wiper arm 14 pivotswith respect to the resistive surface 11 and the length of wiper arm 14are selected so that wiper contact 15 will effectively conductivelycontact electrodes 12 or 13 at degrees diametrically opposite shaftpositions for shaft 16.

FIGURE lb shows a simplified side view of the resolver of FIGURE 1a(with the wiper arm at a different position) and identical referencenumerals are used for clarity. The resistive coating is shown energizedvia electrodes 12 and 13 by a voltage source 17. Although the voltagesource 17 is shown as of the DC. type, it should be clear that followingthe teachings of the present invention the source could also be of theAC. type.

Wiper contact 15 is connected to one input of a summing amplifier 19 andanother input of that same summing amplifier is shown connected tovoltage source 17 in a manner such that the summing amplifier would bereceiving a voltage of approximately one-half that which is appliedacross electrodes 12 and 13. Assuming uniformity in the resistivecoating 11, this will be equal in magnitude to the voltage adjacent thepivot point C of wiper arm 14. When this voltage is inverted byconventional inverter 20 and applied to summing amplifier 19, the outputof amplifier 19 will have a sine voltage variation for a given rotationof shaft 16 as that shown in FIGURE 10.

The cooperation of the resistive coating 11 with the wiper contact 15while shaft 16 is being rotated will be such that a relatively highresolution is obtained in the voltage variation for a given shaftrotation. Moreover, the mechanical construction of the resolver is verysimple and the torque loading on shaft 16 is uniform throughout 360degrees.

For a particular position of the wiper contact as shown in FIGURE 1a,the resistance measured at point D between point D and a horizontal linethrough point C divided by the resistance from the edge of coatingsurface 11 to point C will be proportional to the sine of the angle 0.As indicated hereinabove, it is also important in an electricalresistance resolver to be able to obtain a cosine function of the shaftangle of the shaft driving that resolver. It is a further teaching ofthe present invention that a second wiper arm and wiper contact can beoriented at 90 degrees from the first wiper arm described in connectionwith FIGURE 1a. FIGURE 2a shows such an arrangement.

In order to simplify the explanation, identical reference numerals areutilized in FIGURE 2a as that utilized in FIGURE 1a whenever possible toillustrate identical functional elements. Identical Wiper arms 26 and 27are mounted to rotate about the same pivot point in a manner such thatthey are displaced by 90 degrees. Assuming that the wiper arms 26 and 27are rotating counter-clockwise as a unit, wiper contact 29 will have avoltage derived thereon which is a sine function and wiper contact 28will have a voltage derived thereon which is a cosine function of theshaft angle of shaft 16. Parallel connectors or electrodes 12 and 13 areshown energized by connecting therebetween to voltage sources 22 and 23in series. Voltage sources 22 and 23 are oriented polarity- Wise to beadditive. Assuming a uniform density of resis- *tive coating 11, thevoltage at the common junction of voltage sources 22 and 23 will beequal to the voltage level in the resistive coating 11 immediatelyadjacent the pivot means. Accordingly, this voltage can be utilized inthe same manner via inverter to provide one of the inputs to each of twoconventional summing amplifiers 30 and 31.

The construction of these conventional summing amplifiers is well knownin the prior art and may be considered to include a summing resistornetwork. Accord:

ingly, the voltage derived on wiper contact 29 may be applied to summingamplifier 31 via one of its inputs and compared with the referencevoltage for deriving a voltage shaft angle characteristic such as shownin FIGURE 2b as waveform A which is commensurate with the sine functionof the rotation of shaft angle. Similarly, the voltage derived on wipercontact 28 may be applied to one of the inputs of summing amplifier 30and compared with the reference voltage provided by inverter 20 forderiving a voltage which varies in accordance with the cosine of thevarying shaft angle. Waveform B of FIG- URE 2b shows this functionalvoltage variation. Re-

sistors 24 and 25 connected parallel with voltage sources 7 22 and 23are for balancing purposes. Linear amplifiers 40 and 41 connected towiper contacts 28 and 29 are for the purpose of preventing currentloading problems inherent in potentiometer type devices.

Not only will the outputs of summing amplifiers 31 and provide sine andcosine functional voltage relationships with variations of shaft angledriving wiper arms 26 and 27, but the polarity of the output signalswill be indicative of the-quadrant through which the wiper assembly ispassing. FIGURE 2c shows four possible polarity combinations which willbe usable to determine the quadrant as the practical applications of theteachings of the present invention require such information in systemusage. Moreover, since both sine and cosine functional voltagerelationships are available for various shaft angles, the application ofthis analog information into a conventional analog division circuit 32is all that is necessary to derive a tangential type functional voltagerelationship, such as may be required in a system application. While thevoltage analog division circuit 32 may take various forms, one suchcircuit suitable for use in practicing the present invention isdescribed and explained in detail on page 124 et seq. in the publicationtitled Introduction to Analogue Computers by C. A. A. Wass, 1955edition, published in the United States by McGraw- Hill Inc.

As those skilled in the art will recognize, the tangent function may beobtained by dividing a sine functional voltage by a cosine functionalvoltage and the co-tangent functional relationship may be obtained by aninversion of that analog process. Maximum use of the known trigonometricidentities plus conventional analog computing circuits can provide forsubstantial system application of a resistive resolver of a type builtaccording to the teachings of the present invention.

While the voltage sources described hereinabove in the specification anddrawings have been of the DC. type, it should be clear that in either ofthe embodiments an AC. voltage supply might be used as required for apractical application. Obviously, the summing and amplifier circuitswould have to be modified to accommodate this modification.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formand details may be made therein without departing from the spirit andscope of the invention.

What is claimed is:

1. A shaft angle electrical resolver for deriving electrical signalscommensurate with trigonometric functions of a shaft angle comprising ashaft rotatable through 360 degrees, a fiat surface having a resistivecoating placed thereon of a predetermined uniform resistivity per unitarea, a pair of spaced parallel conductive electrodes fas tened to andconductively cooperative with said resistively coated surface, a firstwiper arm pivotally mounted at one extremity in pivotal relationshipwith the plane of said resistively coated surface and rotatable through360 degrees in accordance with the angular position of said shaft, asecond wiper arm piv-otally mounted at one extremity in pivotalrelationship with the plane of said resistively coated surface androtatable through 360 degrees in accordance with the angular position ofsaid shaft, said first and second wiper arms being displaced degreeswith respect to each other, a wiper contact mounted at the otherextremity of each of said Wiper arms for maintaining a slidableconductive contact on said resistive coating, the position of saidpivotal mounting of each of said w-iper arms and the length of saidwiper arms being selected .so that each of said wiper contacts makesphysical conductive contact alternately with said parallel electrodes atdegree angular positions of said shaft, means for applying a voltageacross said parallel conductive electrodes, the wiper contact of saidfirst wiper arm having a voltage derived thereon commensurate with thesine function of the angle of rotation of said shaft, the wiper contactof said second arm having voltage derived thereon which is a cosinefunction of the angular rotation of said shaft, a first and secondsumming amplifier, each amplifier having at least two summing inputs,said first summing amplifier having its first summing input connected tothe wiper contact on which is derived the sine voltage functionalvariation and its other summing input connected to a voltage sourcewhich is equal in magnitude and opposite in polarity to the voltagelevel present in the resistive coating immediately adjacent the pivotalmounting of the wiper arms, the second summing amplifier having itsfirst summing input terminal connected to the wiper contact on which isderived the cosine function of the rotation of said shaft angle, theother of said summing inputs of said summing amplifier being connectedto a voltage source equal in magnitude and opposite in polarity to thevoltage level in the resistive coating point immediately adjacent thepivotal mounting of said arms, the output voltages of said first andsecond summing amplifiers being indicative of the magnitude of the shaftangle and the quadrant through which said shaft angle is being rotated.

2. A shaft angle electrical resolver for deriving electrical signalscommensurate with trigonometric functions of a shaft angle comprising ashaft rotatable through 360 degrees, a flat surface having a resistivecoating placed thereon of a predetermined uniform resistivity per unitarea, a pair of spaced parallel conductive electrodes fastened to andconductively cooperative with said resist-ively coated surface, a firstwiper arm pivotally mounted at one extremity in pivotal relationshipwith the plane of said resistively coated surface and rotatable through360 degrees in accordance with the angular position of said shaft, asecond wiper arm pivotally mounted at one extremity in pivotalrelationship with the plane of said resistively coated surface androtatable through 360 degrees in accordance with the angular position ofsaid shaft, said first and second wiper arms being displaced 90 degreeswith respect to each other, a wiper contact mounted at the otherextremity of each of said wiper arms for maintaining a slidableconductive contact on said resistive coating, the position of saidpivotal mounting of each of said wiper arms and the length of said wiperarms being selected so that each of said wiper contacts make physicalconductive contact alternately with said parallel electrodes at 180degree angular positions of said shaft, means for applying a voltageacross said parallel conductive electrodes, the wiper contact of saidfirst wiper arm having a voltage derived thereon commensurate with thesine function of the angle of rotation of said shaft, the wiper contactof said second arm having voltage derived thereon which is a cosinefunction of the angular rotation of said shaft, a first and secondsumming amplifier, each amplifier having at least two summing inputs,said first summing amplifier having its first summing input connected tothe wiper contact on which is derived the sine voltage functionalvariation and its other summing input connected to a voltage sourcewhich is equal in magnitude and opposite in polarity to the voltagelevel present in the resistive coating immediately adjacent the pivotalmounting of the wiper arms, the second summing amplifier having itsfirst summing input terminal connected to the wiper contact on which isderived the cosine function of the rotation of said shaft angle, theother of said summing inputs of said summing amplifier being connectedto a voltage source equal in magnitude and opposite in polarity to thevoltage level in the resistive coating point immediately adjacent thepivotal mounting of said wiper arms.

3. A shaft angle electrical resolver as set forth in claim 2 whereinthere is also included an analog division circuit connected toreceivevoltage inputs from said first and second summing amplifiers for thepurpose of deriving a tangential type trigonometric voltage variationwith respect to changes of the angular rotation of said shaft.

4. A shaft angle electrical resolver for deriving a portion of atrigonometric function of a given shaft angle comprising a shaft, a flatsurface having a resistive coating placed thereon of a predetermineduniform resistivity per unit area, a pair of spaced parallel conductiveelectrodes fastened to and conductively cooperating with said resistivecoated surface, a wiper arm pivotally mounted on said resistive coatedsurface and electrically insulated therefrom and rotatable in accordancewith said shaft angle, a wiper contact mounted on the end of said wiperarm for maintaining a slidable conductive contact on said resistivecoating, the position of said pivotal mounting and the length of saidwiper arm being selected so that said wiper contact makes effectiveconductive contact alternately with the two parallel electrodes at 180degrees angular positions of said shaft, said shaft driving said Wiperbeing rotatable through 360 degrees, a source of electrical energy beingconductively connected across said pair of electrodes, a summingamplifier having at least two summing inputs, one of said summing inputsbeing conductively connected to said wiper contact, the other of saidsumming inputs being connected to an electrical energy source equal involtage and opposite in polarity to that present in the resistivecoating immediately adjacent said shaft position of said wiper arm, theoutput of said summing amplifier means providing an electrical signalwhich is a sinusoidal function of the angular position of said shaft.

5. A shaft angle electrical resolver for deriving electrical signalscommensurate with trigonometric functions of a shaft angle comprising ashaft rotatable through 360 degrees, a fiat surface having a resistivecoating placed thereon of a predetermined uniform resistivity per unitarea, a pair of spaced parallel conductive electrodes fastened to andconductively cooperative with said resistively coated surface, at leastone wiper arm pivotally mounted at one extremity in pivotal relationshipwith the plane of said resistively coated surface and rotatable through360 degrees in accordance with the angular position of said shaft, awiper contact mounted on the other extremity of each of said wiper armsfor maintaining a slidable conductive contact on said resistive coating,the position of said pivotal mounting of each of said wiper arms and thelength of each of said wiper arms being selected so that each of saidwiper contacts effectively makes physical conductive contact alternatelywith the two parallel electrodes at 180 degrees angular positions ofsaid shaft, said pair of spaced parallel directive electrodes havingapplied thereacross a voltage source, a summing amplifier having atleast two summing inputs, one of said summing inputs being conductivelyconnected to a wiper contact, the other of said summing inputs beingconnected to an electrical energy source equal in voltage and oppositein polarity to that present in the resistive coating immediatelyadjacent said shaft position of said wiper arm, the output of saidsumming amplifier means providing an electrical signal which is asinusoidal function of the angular position of said shaft.

References Cited by the Examiner UNITED STATES PATENTS 2,457,178 12/1948 Richardson 338- 2,653,206 9/ 1953 Montgomery 338--90 2,764,657 9/1956 Rosen-tha-l 33890 2,864,924 12/1958 Mayer 33889 2,979,681 4/1961Brown 33889 3,046,510 7/1962 Williams et al 33889 3,109,128 10/1963Pruden et a1. 235-186 MALCOLM A. MORRISON, Primary Examiner. I.KESCHNER, Assistant Examiner.

4. A SHAFT ANGLE ELECTRICAL RESOLVER FOR DERIVING A PORTION OF ATRIGONOMETRIC FUNCTION OF A GIVEN SHAFT ANGLE COMPRISING A SHAFT, A FLATSURFACE HAVING A RESISTIVE COATING PLACED THEREON OF A PREDETERMINEDUNIFORM RESISTIVITY PER UNIT AREA, A PAIR OF SPACED PARALLEL CONDUCTIVEELECTRODES FASTENED TO AND CONDUCTIVELY COOPERATING WITH SAID RESISTIVECOATED SURFACE, A WIPER ARM PIVOTALLY MOUNTED ON SAID RESISTIVE COATEDSURFACE AND ELECTRICALLY INSULATED THEREFROM AND ROTATABLE IN ACCORDANCEWITH SAID SHAFT ANGLE, A WIPER CONTACT MOUNTED ON THE END OF SID WIPERARM FOR MAINTAINING A SLIDABLE CONDUCTIVE CONTACT ON SAID RESISTIVECOATING, THE POSITION OF SAID PIVOTAL MOUNTING AND THE LENGTH OF SAIDWIPER ARM BEING SELECTED SO THAT SAID WIPER CONTACT MAKES EFFECTIVECONDUCTIVE CONTACT ALTERNATELY WITH THE TWO PARALLEL ELECTRODES AT 180DEGREES ANGULAR POSITIONS OF SAID SHAFT, SAID SHAFT DRIVING SAID WIPERBEING ROTATABLE THROUGH 360 DEGREES, A SOURCE OF ELECTRICAL ENERGY BEINGCONDUCTIVELY CONNECTED ACROSS SAID PAIR OF ELECTRODES, A SUMMINGAMPLIFIER HAVING AT LEAST TWO SUMMING INPUTS, ONE OF SAID SUMMING INPUTSBEING CONDUCTIVELY CONNECTED TO SAID WIPER CONTACT, THE OTHER OF SAIDSUMMING INPUTS BEING CONNECTED TO AN ELECTRICAL ENERGY SOURCE EQUAL INVOLTAGE AND OPPOSITE IN POLARITY TO THAT PRESENT IN THE RESISTIVECOATING IMMEDIATELY ADJACENT SAID SHAFT POSITION OF SAID WIPER ARM, THEOUTPUT OF SAID SUMMING AMPLIFIER MEANS PROVIDING AN ELECTRICAL SIGNALWHICH IS A SINUSOIDAL FUNCTION OF THE ANGULAR POSITION OF SAID SHAFT.